1. Field of the Invention
The invention relates to a looping machine for the looping of objects such as stacks of newspapers, magazines or any other stacked goods such as packages, for instance cardboxes and the like.
2. Background Art
A looping machine for this purpose is described for instance in the co-pending U.S. patent application Ser. No. 08/785,129 (now U.S. Pat. No. 5,791,238). In addition to the components notoriously present in these equipments, namely a machine frame, work table, strap guiding frame for guiding the strap as a loose loop around the object to be looped, an insertion device for inserting the strap into the strap guiding frame and a withdrawal device for withdrawing the strap from the strap guiding frame and for slinging the strap around the object to be looped, this looping machine also comprises a device for tensioning the looping strap around the object in dependence on the height of a stack. Tensioning in dependence on the height of a stack is of advantage in this connection, since the looping strap must bundle the stack tightly, but tensioning must be the stronger, the softer, i.e. the more compressible, the goods are that form the stack. As a rule, the compressibility of a stack increases with the height of the stack and the number for instance of newspapers in a stack growing. This means that strong tensioning must be ensured in the case of a high stack, whereas virtually no tensioning may occur in the case of very low stacks or when a single newspaper is looped, since this would lead to the paper coiling up.
In the tensioning device according to the prior patent application mentioned above, a complicated mechanical construction is provided for adjusted tensioning in dependence on the height of a stack. A pivotal rocker lever is available, which comprises a control ramp and is adjustable by way of a mechanical device detecting the height of a stack by touch contact. This mechanical touch contact device is for instance a leverage mechanism disposed between the pressing beam which compresses the stack to be looped before the looping strap is fitted around, and the pivotal rocker lever which has a control ramp. The latter actuates a control lever for a clamping lever which is pivotally articulated to the tension lever of the tensioning device, this tension lever producing the tensioning effect. The control lever controls the clamping lever in such a way that when the height of a stack decreases, blocking of the clamping device for fixing the strap is increasingly retarded and the tensioning length of the looping strap is reduced.
In addition to the high mechanical requirements, the known tensioning device has further drawbacks. For instance, the tensioning effect is only varied by adjustment of the tensioning length. Furthermore, only a proportional dependence between the product height and the tensioning length is attainable so that more complex dependencies are not achievable.